They wouldn't be. We limit ourselves to current or near current technology for these analysis or you can easily get into the realms of hypotheticals very easily. If you say that the laws of thermodynamics don't apply to aliens because they have more advanced physics then the sky becomes the limit. So you have to stick by your own rule book when you imagine, so it'd be more appropriate to say that there is unlikely to be Dyson swarms near us that were built by aliens with a similar understanding of physics. For all we know the popular way that they gather energy is harvesting photons from within the star itself, stick a giant straw into a star and just drink away the photons.

I'm not suggesting that we speculate into high fantasy. What I'm getting at is that we can't come to a conclusion about whether advance civilizations exist or what they might look like to us. So quite the opposite of realms of hypotheticals really.